Circuit Disconnection Diagnosis — FRCA Final MCQ

Instant feedback + full explanation. One question, done properly.

EasyAnaesthetic Equipment & SafetyCircuit Disconnection DiagnosisFRCA Final

After 30 minutes of stable volume-controlled ventilation through a tracheal tube with a sustained capnography trace, the ventilator alarm sounds. The capnograph abruptly becomes flat, peak airway pressure is very low, and the delivered tidal volume falls to almost zero. The SpO2 subsequently begins to fall, and there are no breath sounds bilaterally. What is the most likely cause?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: B — Complete circuit disconnection

A complete circuit disconnection causes loss of gas delivery to the patient, producing an abrupt flat capnograph, very low airway pressure, negligible delivered tidal volume and absent bilateral breath sounds; desaturation follows after oxygen reserves are consumed. Oesophageal intubation must always be excluded when there is no sustained exhaled CO2, but it is unlikely after 30 minutes of previously stable tracheal ventilation and does not specifically explain the simultaneous low-pressure alarm. Tension pneumothorax and bronchospasm usually increase airway pressure; pneumothorax usually causes asymmetric breath sounds, while bronchospasm commonly produces expiratory wheeze and a sloping capnogram. Cardiac arrest markedly reduces end-tidal CO2, but mechanical inflation pressures and ventilated breath sounds do not abruptly disappear.

Reference: Royal College of Anaesthetists. Guidelines for the Provision of Anaesthesia Services for the Perioperative Care of Elective and Urgent Care Patients, section 7.4, 2025. https://www.rcoa.ac.uk/gpas/chapter-2; supported by Association of Anaesthetists, Recommendations for standards of monitoring during anaesthesia and recovery, Breathing systems and Alarms sections, 2015. https://www.rcoa.ac.uk/sites/default/files/documents/2019-11/Guideline_standards_of_monitoring_anaesthesia_recovery_2015_final%20%281%29%20to%20be%20uploaded.pdf